by Chris Woodford. Last updated: July 12, 2014.
Have you ever tried writing with a beam
of light? Sounds
impossible, doesn't it, but it's exactly what a laser printer does
when it makes a permanent copy of data (information) from your
computer on a piece of paper. Thanks to sci-fi and spy movies, we
tend to think of lasers as incredibly
powerful light beams
that can slice through chunks of metal or blast enemy spaceships into
smithereens. But tiny lasers are useful too in a much
more humdrum way: they read sounds and video clips off the discs in
CD and DVD players and they're
vital parts of most office computers printers. All set? Okay, let's take a closer look at how laser printers
Photo: A compact laser printer doesn't look that different to an
inkjet printer, but it puts ink on the page in a completely different way.
An inkjet printer uses heat to squirt drops of wet ink from hot, syringe-like tubes, while a laser printer
uses static electricity to transfer a dry ink powder called toner.
Laser printers are similar to photocopiers
Laser printers are a lot like photocopiers and use the same basic technology.
Indeed, as we describe later in this article, the first laser printers were
actually built from modified photocopiers. In a photocopier, a bright light is used to make an exact copy of a printed page. The light
reflects off the page onto a light-sensitive drum;
(the effect that makes a balloon stick to your clothes if you rub it a
few times) makes ink particles stick to the drum; and the ink is then
transferred to paper and "fused" to its surface by hot
rollers. A laser printer works in almost exactly the same way, with
one important difference: because there is no original page to copy,
the laser has to write it out from scratch.
Imagine you're a computer packed full of data. The information you
store is in electronic format: each piece of data is stored
electronically by a microscopically small switching device called a
transistor. The printer's job is
to convert this electronic
data back into words and pictures: in effect, to turn electricity
into ink. With an inkjet printer,
it's easy to see how that
happens: ink guns, operated electrically, fire precise streams of ink
at the page. With a laser printer, things are slightly more complex.
The electronic data from your computer is used to control a laser
beam—and it's the
laser that gets the ink on the page, using static electricity in a
similar way to
Who invented laser printers?
Until the early 1980s, hardly anyone had a personal or office computer; the few people who did made
"hardcopies" (printouts) with dot-matrix printers. These relatively slow
machines made a characteristically horrible screeching noise because they used a grid of tiny metal
needles, pressed against an inked ribbon, to form the shapes of letters, numbers, and symbols
on the page. They printed each character individually, line by line, at a typical speed of about 80 characters
(one line of text) per second, so a page would take about a minute to print. Although that sounds
slow compared to modern laser printers, it was a lot faster than most people could bash out letters
and reports with an old-style typewriter (the mechanical or electric keyboard-operated
printing machines that were used in offices for writing letters before affordable computers made them obsolete). You still occasionally see bills and address labels printed by dot-matrix; you can always tell because the print is relatively crude and made up of very visible dots. In the mid-1980s, as computers became more popular with small businesses, people wanted machines that could produce letters and reports as quickly as dot-matrix printers but with the same kind of print quality they could get from old-fashioned typewriters. The door was open for laser printers!
Fortunately, laser-printing technology was already on the way. The first laser printers had been developed in the late 1960s by Gary Starkweather of Xerox, who based his work on the photocopiers that had made Xerox such a successful corporation. By the mid-1970s, Xerox was producing a commercial laser printer—a modified photocopier with images drawn by a laser—called the Dover, which could knock off about 60 pages a minute (one per second) and sold for the stupendous sum of $300,000. By the late 1970s, big computer companies, including IBM, Hewlett-Packard, and Canon, were competing to develop affordable laser printers, though the machines they came up with were roughly 2–3 times bigger than modern ones—about the same size as very large photocopiers.
Two machines were responsible for making laser printers into mass-market items. One was the LaserJet, released by Hewlett-Packard (HP) in 1984 at a relatively affordable $3495. The other, Apple's LaserWriter, originally cost almost twice as much ($6995) when it was launched the following year to accompany the Apple Macintosh computer. Even so, it had a huge impact: the Macintosh was very easy to use and, with relatively inexpensive desktop-publishing software and a laser printer, it meant almost anyone could turn out books, magazines, and anything and everything else you could print onto paper. Xerox might have developed the technology, but it was HP and Apple who sold it to the world!
The first laser printer
Dipping into the archives of the US Patent and Trademark Office, I've found one of Gary Starkweather's original laser-printer designs, patented on June 7, 1977. To make it easier to follow, I've colored it in and annotated it more simply than the technical drawing in the original patent (if you wish, you can find the full details filed under
US Patent 4027961: Copier/Raster Scan Apparatus).
What we have is essentially a laser scanning unit (colored blue) sitting on top of a fairly conventional, large office
photocopier (colored red). In Starkweather's design, the laser scanner slides on and off the glass window of the photocopier
(the place where you would normally put your documents, face down), so the same machine can be used as either a laser printer
or a copier—anticipating all-in-one office machines by about 20–25 years.
How does it work?
- The laser scanner creates the image.
- The image is beamed through the glass copier window into the copier mechanism underneath.
- The image is reflected by a mirror.
- A lens focuses the image.
- A second mirror reflects the image again.
- The image is transferred onto the photocopier belt.
- A developer unit converts the image into printable form.
- The printable image is transferred to the paper.
- The fuser permanently seals the image onto the page, which emerges into the collecting rack at top of the machine.